Heat developable light-sensitive materials and image producing processes associated therewith are well known in the art as described in "The Basic Photographic Engineering", Corona Publishing K.K., pages 553-555 (1979); "Image Information", page 40 (April, 1978); and "Neblett's Handbook of Photography and Reprography", 7th Ed., Van Nostrand Reinhold Company, pages 32-33.
Exemplary methods for producing color images include a method using a dye-releasing material in the form of a coupler (see U.S. Pat. Nos. 3,531,286; 3,761,270; and 4,021,240; Belgian Pat. No. 802,519; Research Disclosure, pages 31-32, September 1975); a method using a dye-releasing material in the form of a compound having a nitrogen-containing heterocyclic radical incorporated in its dye moiety (see Research Disclosure, pages 54-58, May 1978); a method using silver dye bleaching (see Research Disclosure, pages 30-32, April 1976, ibid, pages 14-15, December 1976, and U.S. Pat. No. 4,022,617); and a method using a leuco dye (see U.S. Pat. Nos. 3,985,565 and 4,022,617).
These methods, however, have their own shortcomings and commonly suffer from the problem that development takes a relatively long time and the resulting image is markedly fogged with a low maximum density (Dmax).
In order to solve this problem, U.S. Pat. No. 4,500,626 proposes to use a reducing dye-releasing material capable of releasing a hydrophillic dye. This method has succeeded in overcoming the technical problems of the prior art to a great extent.
There is still the need for the development of an improved light-sensitive material which can be heat developed to a higher maximum density with less fogging at a lower temperature within a shorter heating time than the material described in the above-identified U. S. Patent.